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Fine Thread High Hex Nut Dimensions (ISO 8674, M8x1 to M36x3)

Guide · Updated October 28, 2026

ISO 8674 covers hexagon high nuts, style 2, with metric fine pitch thread, product grade A up to M16 and grade B from M18. Hex, corners and bearing face match ISO 8673; only the height is greater. Values agree across three sources: the ISO 8674:2023 preview table (M8 to M16 in full, plus the 2023 pitch pairings), the ISO 8674:2012 preview tables (every size M8 to M36) and the GlobalFastener ISO 8674 table. The s min values for M18, M22, M27 and M33 come from GlobalFastener and match the shared hex in ISO 8673. Not shown: transition diameter da, because the 2023 edition changed da max (for example M12 12.96 vs 13.00 mm). Skipped: M39x3 and the M18x2 and M22x2 pitches added in 2023, since only one source lists their heights. One catalog table we checked lists M12 e min as 20.3 and mw as 9.62; the ISO tables say 20.03 and 9.26, so we used the ISO values.

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Step by step

Confirm fine pitch: Check pitch with a thread gage. An M12x1.5 nut will not run on a coarse M12x1.75 bolt.
Pick the wrench: Same hex as ISO 8673 and ISO 4033: M8 13 mm, M10 16 mm, M12 18 mm, M16 24 mm, M20 30 mm, M24 36 mm.
Check the height: Use m max for bolt length math. ISO 8674 is taller than ISO 8673: M12 12.00 vs 10.80 mm, M20 20.30 vs 18.00 mm.
Check the bearing face: Seat diameter must clear dw min (M16 is 22.49 mm) for full bearing.
Match the property class: Style 2 height lets the nut carry higher class bolts; match nut class to the bolt per ISO 898-2.
Leave thread past the nut: Run at least 2 full threads past the nut face.

ISO 8674 fine thread high hex nut dimensions (mm)

Columns: thread size x pitch, width across flats s max and min (s max is the wrench size), nut height m max, m min, wrenching height mw min, width across corners e min, bearing face diameter dw min. Sizes in parentheses are non-preferred in ISO 8674:2023.

Size | s max | s min | m max | m min | mw min | e min | dw min
M8x1 | 13.00 | 12.73 | 7.50 | 7.14 | 5.71 | 14.38 | 11.63
M10x1.25 / (M10x1) | 16.00 | 15.73 | 9.30 | 8.94 | 7.15 | 17.77 | 14.63
M12x1.5 / (M12x1.25) | 18.00 | 17.73 | 12.00 | 11.57 | 9.26 | 20.03 | 16.63
(M14x1.5) | 21.00 | 20.67 | 14.10 | 13.40 | 10.72 | 23.36 | 19.64
M16x1.5 | 24.00 | 23.67 | 16.40 | 15.70 | 12.56 | 26.75 | 22.49
(M18x1.5) | 27.00 | 26.16 | 17.60 | 16.90 | 13.52 | 29.56 | 24.85
M20x2 / (M20x1.5) | 30.00 | 29.16 | 20.30 | 19.00 | 15.20 | 32.95 | 27.70
(M22x1.5) | 34.00 | 33.00 | 21.80 | 20.50 | 16.40 | 37.29 | 31.35
M24x2 | 36.00 | 35.00 | 23.90 | 22.60 | 18.08 | 39.55 | 33.25
(M27x2) | 41.00 | 40.00 | 26.70 | 25.40 | 20.32 | 45.20 | 38.00
M30x2 | 46.00 | 45.00 | 28.60 | 27.30 | 21.84 | 50.85 | 42.75
(M33x2) | 50.00 | 49.00 | 32.50 | 30.90 | 24.72 | 55.37 | 46.55
M36x3 | 55.00 | 53.80 | 34.70 | 33.10 | 26.48 | 60.79 | 51.11

Style 2 vs style 1 fine nut

An M12x1.5 ISO 8674 nut is 12.00 mm max high; the ISO 8673 style 1 nut is 10.80 mm. Both take an 18 mm wrench, so measure height to tell them apart.

Worked example: bolt length for an M16x1.5 high nut

Grip 25 mm, nut m max 16.40 mm, plus 2 threads at 1.5 mm = 3.0 mm. Total 44.4 mm, so an M16x1.5 x 45 works.

Common problems

Coarse bolt, fine nut: it starts, then binds. Check pitch first.
Mixed bins: style 1 and style 2 look the same from above. Check height.
M10 and M20 pitch changed between the 2012 and 2023 editions' preferred lists. Read the label.

FAQ

What is the difference between ISO 8674 and ISO 8673?

Same hex, corners and bearing face size for size. ISO 8674 (style 2) is taller: M8 7.50 vs 6.80 mm, M16 16.40 vs 14.80 mm, M36 34.70 vs 31.00 mm max.

What is the difference between ISO 8674 and ISO 4033?

Same style 2 height and hex size for size. ISO 8674 has metric fine pitch thread; ISO 4033 has coarse thread.

What wrench fits an M16x1.5 high hex nut?

24 mm.

How tall is an M20x1.5 ISO 8674 nut?

20.30 mm max, 19.00 mm min.

Which pitch is preferred?

M10x1.25, M12x1.5 and M20x2 are first choice in ISO 8674:2023; M10x1, M12x1.25, M20x1.5 and sizes in parentheses are non-preferred. The 2012 edition listed M10x1 and M20x1.5 as preferred, so older stock and catalogs differ.

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